1.
Heat the oven to 350°F. Heat the oil in a large deep oven-proof skillet
over medium-high heat until it shimmers. Salt and pepper the ribs and
cook them, in batches, until they are nicely browned on all sides, about
20 minutes.

2. Remove the ribs and add the onion, carrot, celery, garlic, 2 sprigs
of the thyme, and salt and pepper to the skillet. Cook, stirring occasionally,
until the vegetables begin to soften, about 5 minutes, then add the peppers
(if you are using canned peppers, add them with the vegetables in step
4). Continue cooking until the vegetables are tender and browned, 5 to
10 minutes more.

3. Return the ribs to the skillet. Add the vinegar and enough stock to
come up the sides but not over the ribs. Bring the braising liquid to
a simmer. Add the tarragon and the remaining thyme, then transfer the
skillet to the oven and cook at a very gentle simmer (just an occasional
bubble) for 1 hour. Turn the ribs and continue cooking until the meat
is tender and comes easily away from the bone, about 1 1/2
hours more.

4. Transfer the ribs and vegetables to a plate. Bring the braising liquid
to a simmer and skim off the fat. Reduce the liquid slightly (just so
it has a little body), then return the ribs and vegetables to the skillet.
Simmer just long enough to reheat the ribs, then serve.